The present invention relates to a method for access from subscriber terminals in different service classes to access channels in a communications system having different service classes, and to a correspondingly designed communications system.
Currently existing communications systems are being continually improved and new, upgraded or optimized services are continuously being provided in these communications systems, and are expressed in different service classes in the corresponding communications systems. Services such as these may represent specific services which a subscriber to the communications system can use directly, such as speech, data or multimedia communication, or accompanying services such as a call answering function or the like. However, it is also possible to provide services which relate to the internal procedures in the communications system, such as the nature, number and capacity of communications channels, the way in which data is passed on or processed, or the like.
WO 98/24250 A2 describes a communications system in which a mobile station, which is referred to as VIP MS, has its own access channel, by which it receives exclusive access to special packet data channels, as required.
One example of this is mobile radio systems, in which second-generation mobile radio systems are currently operated, in particular such as GSM or GPRS, and third-generation mobile radio systems are specified, in particular such as UMTS or UTRAN. In this case, networks are also envisaged which form an interface function between second- and third-generation mobile radio systems, in particular such as GERAN networks, and which thus have facilities which allow services for the second generation and third generation of mobile radio systems in parallel. In this case, the radio transmission part (radio interface) of the GERAN network is designed on the basis of the second generation of mobile radio systems, while the landline network part of the GERAN network is designed on the basis of the third generation of mobile radio systems. A GERAN system thus supports not only the A interface for line-switched connections and the Gb interface for packet-switched connections for the second generation, but also the lups interface for package-switched connections and the lucs interface for line-switched connections for the third generation.
By way of example, the provision of bidirectional communications channels is intended as a service in one of the first service classes—corresponding to the second generation of mobile radio systems—for GERAN networks of this type, that is to say channels in the downlink direction from the communications system to a subscriber terminal and in the uplink direction from the subscriber terminal to the communications system, which channels are coupled to one another and have a defined frequency separation (45 MHz) and a defined separation in the time slot structure (3 time slots) for the TDMA radio interface for the GERAN network. On the other hand, the service may also include as a further service class unidirectional communications channels in the uplink direction or downlink direction, which are not coupled to any corresponding second channel and thus allow greater flexibility for assignment of transmission capacities to communications connections. This makes it possible to make better use of the total available transmission capacities, allowing more communications connections to be supplied with the necessary transmission capacity than in the case of systems with bidirectional channels. These measures are described, by way of example, in Tdoc 2e00–126 “GERAN Physical Sub-Channels”, ETSI SMG2 Working Session on EDGE, Seattle, Wash. USA, May 8–12, 2000.
Specifically, subscriber terminals can access communications systems via specific access channels. For example, a specific, common signaling channel (common control channel CCCH) is provided in mobile radio systems for this purpose, and is in the form of an access channel (random access channel RACH). However, previous access methods have not allowed a subscriber terminal to be assigned to the services in good time in that service class which is necessary or optimum for the service class of that terminal overall or the service currently being requested by the subscriber terminal. In fact, such optimized assignment is carried out only in a second step after a previously complete access by the subscriber terminal to the communications system, and this increases the signaling complexity or may even make it necessary for the terminal to access the communications system once again, on this occasion specifically directed at the appropriate services in the appropriate service class (directed retry).